The present invention relates to a transmission unit installed to a hybrid vehicle which is equipped with an internal combustion engine and an electric motor as a driving force generator.
Various types of hybrid vehicles have been proposed in order to respond to social demands in view of environmental protection and fuel economy. Most of the proposed hybrid vehicles are arranged to comprise an electric motor and an internal combustion engine as a motive power generator. When such a hybrid vehicle is produced, it is preferable to employ a conventional transmission without changing a basic layout in view of cost saving. For example, Japanese Patent Provisional Publication No. 9-329228 discloses a continuously variable transmission (CVT) arranged as shown in FIG. 12. This CVT is constituted by a torque converter chamber 101 defined by the first housing 113 and a first partition wall 116, a planetary gear chamber 102 defined by a second housing 114, the first partition wall 116 and a second partition wall 117, and a transmission chamber 103 defined by a third housing 115 and the second partition wall 117.
Rotational power of an engine is inputted to a torque converter 110 provided in the torque converter chamber 101. An output from the torque converter 110 is inputted into the planetary gear chamber 102 to changeover the rotational direction between the forward or reverse direction. Then, the power is inputted from the torque converter 110 to a transmission 112 of the transmission chamber 103. The transmission 112 comprises a belt-type CVT which transmits the output rotation of the planetary gear 111 through a driver pulley 112a and a belt 112c to a follower pulley 112b. The hydraulic pressure outputted from a control valve unit is supplied to an axial oil passage 123 of the driver pulley 112a through a case 120, an oil pump 121 and an input shaft 122. Further, the hydraulic pressure is supplied to a driver pulley cylinder chamber 124 of the driver pulley 112a to control a transmission ratio.
However, when such a conventional transmission unit for an engine-drive vehicle is adapted as that for a hybrid vehicle without changing the basic layout, it is first planed to put an electromagnetic clutch in the torque converter chamber 101 and a motor in the planetary gear chamber 102. In such a plan, it is necessary to locate the electromagnetic clutch and the motor in a dry chamber in which oil for control and lubrication is not entered. Further, a hybrid vehicle is put in a running state even when the engine is stopped. Therefore, it is necessary to provide an electric oil pump for supplying hydraulic pressure during such engine-stopped running state.
In other way, an electric oil pump may be installed outside of the transmission unit. For example, as disclosed in Japanese Patent Provisional Publication 10-205606, an electric oil pump may be installed outside of a housing of the transmission unit. However, if the electric oil pump is simply installed to the housing, the size of the transmission unit including the electric oil pump becomes large to degrade the installation on a vehicle.
It is therefore an object of the present invention to provide an improved transmission unit which maintains a basic layout of a conventional transmission unit and comprises an electric oil pump.
A transmission unit according to the present invention comprises a hydraulic control valve unit, a housing and an electric oil pump. The hydraulic control valve unit is disposed at a plane parallel to an axis of the transmission unit. The hydraulic control valve unit controls hydraulic pressure for controlling and lubricating a transmission mechanism. The housing has a depressed portion which is contacted with the hydraulic control valve unit, the transmission mechanism of the transmission unit and the hydraulic control valve unit is disposed in said housing. The electric oil pump is disposed on the depressed portion of said housing so that a part of the hydraulic control valve unit is overlapped with a part of the electric oil pump through the depressed portion.